Precipitating metals from solutions.



UNITED STATES Patented. April 5, 1904.

PATENT OFFICE.

CHARLES BUTTERS, OF BERKELEY, CALIFORNIA.

PRECIPITATING METALS FROM SOLUTIONS.

.JPECIFICATION forming part of Letters Patent No. 756,211, dated April5, 1904.

Application filed October 3, 1902. Serial No. 125,750. (No model.)

To all whom it may concern:

' Be it known that I, CHARLES BUTTERS, a citizen of the United States,and a resident of Berkeley, in the county of Alameda and State ofCalifornia, have invented certain new and useful Improvements inPrecipitating Metals from Solutions, of which the following is aspecification.

This invention relates tothe electrolytic method of precipitating orseparating metals from solutions, and more particularly to theprecipitation of gold, silver, copper, and other electronegative metalsfrom cyanid solutions.

It is well known that when metals, such as gold and silver, have beendissolved in solutions, such as potassium cyanid, they may again beseparated from the solution by a suitable electric current, using aninsoluble anode and a suitable surface as a cathode. Also it is wellknown that when the current is of low density the deposit becomes of ahigh regu- 'line nature, adhering more or less firmly to thecathode-surface, while with a high current density the deposit becomesof a loose powdery or slimy nature and may be easily wiped off thecathode-surface. When the deposit is hard, as formed with a low-densitycurrent, considerable difliculty and expense are experienced in removingit from the oathode-surface; but when in a slimy or powdery form thedeposit may be brushed or wiped off without difficulty. Anodes of leadperoxid have been found suitable for this purpose and cathodes of iron,aluminium, or lead have been employed; but it has been found that ironrusts and produces a rough surface, which makes it diflicult to wipe offthe fine slimy deposit. This difficulty was got over by employingaluminium cathodes; but it was found that the aluminium or lead soonbecame brittle and fell to pieces, especially if mercury was present inthe solutions. Now I have found that by employing a cathode of tin or ofmetal coated with tin, such as tinned iron, these difficulties areobviated, and that if the anode is of lead peroxid it is not acted on bythe solution when the current is of the requisite electromotive force toproduce the slimy deposit.

In carrying out my invention I prefer to employ sheets of metal coatedwith tin, such as the so-called tin plates of commerce, and I connectthese in the cyanid solution with an electric generator to formcathodes, while the anodes are of lead peroxid. The anodes and cathodesare usually placed three inches apart, but may be nearer or fartherapart, and the solution containing the metal or metals to be depositedis caused to flow between'the electrodes, preferably in an upward ordownward direction, at a uniform velocity, while an electric current ofhigh density enters the cathode. In practice about 0.5 ampere per squarefoot of cathode is found suitable in most cases; but this may be greateror less, as conditions change. The dissolved metals then deposit in aloose slimy form on the tin cathode-surface and may be removed bybrushing or wiping the plates with a soft material, such as rubber,wood, and the like. This may be conveniently done by removing thecathodes from the solution when the deposit is sufliciently thick or, asusually, by running a wiper'over the plates at intervals of, say, once aday while in position in the solution and allowing the removed slime tosettle to the bottom of the vessel. This slimy deposit is removed fromthe vessel at regular periods, and the'metals are separated and refinedin the usual way.

The apparatus as ordinarily employed in the electrolytic process ofprecipitating in the cyanid-of-gold extraction and the usual method ofprocedure is particularly suitable for this invention.

To obtain the most suitable current density at the cathode, the voltageof the electric current is made to vary with the conductivity of thesolution and the most suitable current is found by gradually increasingor decreasing the electromotive force until the metal deposits justloosely enough to be wiped ofi? easily.

What I call a high-density electric current is that current whichdeposits the metal in this loose form.

What I claim, and desire to secure by Letters Patent, is

1. The improvement in the process of precipitating metals fromsolutions, chiefly cyanid tions which consists in using a cathode havingsmooth surfaces of tin, substantially as described.

In testimony whereof I have hereunto set my hand, at the city of NewYork, in the State of New York, this 1st day of October, 1902.

CHAS. BUTTERS.

In presence of- JOHN S. SEYMOUR, JOHN J. RANAGAN.

